1. Field of the Invention
This disclosure generally relates to a speaker system and a speaker driving circuit and, more particularly, to a hybrid speaker system and a hybrid speaker driving circuit.
2. Description of the Related Art
Presently, speakers can be mainly divided into the coil speaker, the piezoelectric speaker and the capacitive speaker according to different driving methods. The coil speaker is a mature technology and is the most widely used speaker. Generally, an AB class or a D class amplifier is used as a driving circuit for the coil speaker. FIG. 1 shows a schematic diagram of driving a coil speaker CS with an AB class or D class amplifier 9. Based on the operational characteristic of the coil speaker CS, the amplifier 9 has to provide driving signals with low voltage (about 1 to 10 Vrms) and high current (about 0.1 to 1 Ampere).
The capacitive speaker has a superior sound quality than other types of speakers. However, the driving circuit used to drive a capacitive speaker has to provide driving signals with high voltage (more than 100 Vrms) and low current (about 0.1 A), which is just opposite to that used to drive a coil speaker.
Generally speaking, the coil speaker has better operational characteristic in low frequency band while the capacitive speaker has better operational characteristic in middle and high frequency bands. Therefore, it is a choice to improve the sound quality of a speaker system by integrating the coil speaker and the capacitive speaker into a system. However, as the coil speaker and the capacitive speaker have different driving characteristics as mentioned above, it is necessary to propose a driving circuit that can simultaneously drive two types of speakers and a speaker system that uses two different types of speakers.